Parallel-beam scanning for surface patterning of materials

ABSTRACT

A system and method for parallel-beam scanning a surface. An energetic beam source emits an energetic collimated beam which is received by an optical device, comprising: one or more optical media, operable to receive the emitted beam, such as two pairs of coordinated mirrors or a right prism, and at least one actuator coupled to the one or more optical media, and operable to rotate each of the one or more optical media around a respective axis to perform a parallel displacement of the beam in a respective direction, wherein the respective direction, the beam, and the respective axis are mutually orthogonal. The optical device is operable to direct the beam to illuminate a sequence of specified regions of a surface.

FIELD OF THE INVENTION

The present invention relates to the field of manufacture, and moreparticularly to a system and method for patterning of a surface via anenergy beam, such as a semiconductor surface, where the beam causeslocal heating and may be used to effect local melting of the surface ofthe material to cause thermally based effects such as dopant diffusion,oxidation, crystallization, and so forth.

DESCRIPTION OF THE RELATED ART

Surface patterning refers to the creation or generation of patterns onmaterial surfaces. Many methods have been in use for some time,particularly for surface treatment and patterning of semiconductorwafers. For example, diffusion and ion implantation, rapid thermalprocessing (RTP), laser etching, reactive ion etching, epitaxial growth,physical and chemical deposition methods based on sputtering, ChemicalVapor Deposition (CVD), and other techniques have been used inconjunction with masks to select the portions of the surface to betreated. However, these approaches have various problems relating toprecise and controllable patterning when divergent beams are employed,specifically as regards scanning a plane surface.

For example, galvanometer laser beam scanners, e.g., such as thoseprovided by Cambridge Technology Inc., are well known but do not addressthese problems (sufficiently precise control of divergent beams so as toscan a plane surface effectively).

In some prior art approaches, mirrors are used to control the beam. Forexample, in one approach to a mirror-scanning mechanism, twogalvanometer mirrors may be arranged in series with mutually orthogonalrotational axes. The laser beam strikes the first mirror, which reflectsit to the second, which in turn reflects it to the target surface. Ifone assumes that the apparent source of the beam is a fixed pointlocated at the center of a spherical surface, then such a system mayscan uniformly a “spherical rectangle” on the inner surface of thesphere, e.g., a region bounded by two pairs of mutually orthogonalgreat-circle segments. However, this “spherical” scan technique is notadequate for scanning a plane surface; the resulting geometricaldistortion is a serious shortcoming of such an arrangement.

Another problem is that in prior dual mirror systems the apparent sourceposition is not fixed. In other words, as the mirrors rotate on theirrespective axes, the apparent source of the laser beam changes. Saidanother way, in such prior art approaches, the laser beam strikes thefirst mirror at a point on its axis, and then necessarily strikes apoint that moves from side to side across the axis of the second mirror,and so, even in the best case there is still a linear translation of theapparent source. In other words, the apparent source moves along astraight-line segment. This defect has been termed “positional jitter”or “displacement jitter.” (See FIG. 1, described below).

FIG. 1 illustrates a prior art dual mirror arrangement demonstratingsome of the above issues, including positional jitter. As FIG. 1 shows,a beam source, e.g., laser 100, emits a beam 101 which impinges a firstmirror 102 that is rotatable (e.g., via an actuator, such as agalvanometer, etc.) about a vertical axis 103. The first mirror 102reflects the beam 101 to a second mirror 104 that is rotatable about ahorizontal axis 105, which in turn reflects the beam to a target 108.Thus, the first mirror 102 may be used to angularly deflect the beamhorizontally, as indicated by the dashed secondary path of the beam inFIG. 1. Similarly, the second mirror 104 may be used to angularlydeflect the beam vertically, although in FIG. 1, the second mirror isshown in a neutral position, i.e., with no rotation about the horizontalaxis 105. Note that the mirrors could also be swapped, such that thefirst mirror has a horizontal axis of rotation, and the second mirrorhas a vertical axis of rotation.

As FIG. 1 shows, the horizontal deflection of the beam results in achange in apparent beam source position from the target's perspective,denoted as “displacement jitter” in the Figure. In prior art systems,this effect is generally detrimental to accurate beam positioning on thetarget. To stabilize the apparent beam source, it would be necessary tohave the laser beam strike a mirror that is capable of rotation abouttwo orthogonal axes, where the laser strikes the mirror at theintersection of the axes. Such a product exists, being available fromNewport Corporation, Irvine, Calif., as a Fast Steering Mirror (FSM)with two-axis high-bandwidth motion. In this approach, a single mirrordriven by a “voice coil” is capable of both X and Y deflection,employing magnetic forces produced by a solenoid to create the desiredmotion. These mirrors are sometimes used in pairs, where one mirror isused to fine tune beam position (e.g. the Newport BSD-2A Beam Steerer),and a second mirror is used for “beam stabilization” via a feedbacksystem, (both of which suggest a lack of precision in mirror-positioncontrol). This configuration attempts to solve theapparent-source-motion problem but still uses diverging beams and thusdoes not solve the problem of geometrical distortion on a plane surface,e.g., due to non-normal incidence of the beam on the target. In otherwords, this approach also suffers from the “spherical” scanning issuedescribed above.

Another prior art approach called Gas-Immersion Laser Doping (GILD) hasbeen demonstrated at Lawrence Livermore National Laboratories. In thisapproach, a silicon sample is placed in a gas of dopant atoms or ofdecomposable molecules containing dopant atoms. A pattern mask isinterposed between the target surface and a beam source. An energeticlaser, e.g., in the ultraviolet spectrum where surface absorption forsilicon is high, then illuminates the masked surface, melting a thinlayer of surface silicon (where not masked), whereupon liquid-phasediffusion, orders of magnitude more rapid than solid-phase diffusion,leads to a near-uniform density of dopant in the melt, even in the brieftime before refreezing of the silicon surface occurs.

This technique may be used for surface patterning of a semiconductorsubstrate such as monocrystalline Silicon or Germanium or GalliumArsenide or other Periodic Table Group IV elements or Group III-Vcompounds or Group II-VI compounds, or other combinations, as is knownin the art of manufacture of crystalline semiconductor substrates.However, such broad illumination of the masked surface requires verypowerful beam sources, which are substantially expensive and dangerous.

GILD and other alternative methods and systems (with relevantapplications) are more fully described in U.S. Pat. No. 5,346,850, whichis hereby incorporated by reference. Also see K. H. Weiner et al.,“Low-Temperature Fabrication of P+-n Diodes with 300-A Junction Depth,”IEEE Electron Device Lett. vol. 13, no. 7, pp. 369-371 (July, 1992), aswell as P. G. Carey et al., “Fabrication of Submicrometer MOSFET's UsingGass Immersion Laser Doping (GILD)”, IEEE Electron Device Letters, Vol.EDL-7, No. 7, July 1986, U.S. Pat. Nos. 6,680,485; 6,509,217; 6,372,592;5,885,904; each of which is hereby incorporated by reference.

SUMMARY OF THE INVENTION

Various embodiments of a system and method for patterning a surface arepresented. One embodiment of the present invention comprises a scanningUV-laser-beam system for the patterned heat-treating of a surface. It ischaracterized by the following possible benefits:

1. The system may treat an area measuring a fraction of a cm2 to a fewcm2;

2. The system may have a megapixel to gigapixel or greater resolution(i.e. capable of being used to sub-micron effective scanning spot size);

3. The beam may be of high intensity or fluence (sufficient to meltsilicon);

4. The process may be driven by a low-power to medium-power laser, e.g.,a milliwatt laser;

5. The system may use optics that:

-   -   a. may be lens-free, i.e., using reflective media (e.g.,        mirrors) only;    -   b. may be mirror-free, i.e., using transmissive media only;    -   c. have a wide working-distance range from optics to target,        e.g. from approximately one centimeter to one or more meters;        and    -   d. are “straight ahead” in the sense that beam direction is        essentially unidirectional.

First, a beam may be received from an energetic beam source, e.g., by anoptical device, where the beam has an initial direction. The beam sourcemay be any of various types of beam source, such as, for example, a UVlaser or other beam source, one or more UV lamps with a collimator, etc.The beam is preferably a collimated radiation beam. In some preferredembodiments, a laser beam with a wavelength of approximately 193nanometers or 308 nanometers may be used. The beam is preferablyoperable to locally energize an illuminated region of a surface,referred to as a “pixel”, whose size is determined by the beam spotsize, i.e., the beam's cross-sectional area.

The optical device preferably includes one or more elements that arerotatable about one or more respective axes, and which may operate todisplace the beam in a direction orthogonal to the beam, where the beamdisplacement direction and magnitude correspond to the rotation(direction and magnitude). In preferred embodiments, the optical devicecomprises a parallel-beam scanner, various embodiments of which aredescribed below.

One or more optical elements may be rotated about respective axes todisplace the beam in a specified direction orthogonal or normal to thebeam, where the displaced beam is parallel to the received beam.

A respective region of the surface may be illuminated with the displacedbeam, where the respective region corresponds to positions of therotated one or more optical elements. For example, the surface maycomprise a silicon wafer, where the illuminated region may be heated andpossibly melted to effect efficient dopant diffusion into theilluminated region. The dopant may be sourced from the enclosing gas (asin GILD) or from a layer of dopant-containing material, such as heavilydoped silicon (e.g. with Boron or other P-type dopant, or Phorphorous orArsenic or other N-type dopant) deposited using sputter-epitaxy, or aspin-on dopant such as boron or arsenic. Note that as used herein,p-type and n-type semiconductor material may be referred to respectivelyas type-1 and type-2 semiconductor material, or vice versa.

The method elements described above may be repeated to energize aspecified sequence of respective regions of the surface, therebypatterning the surface. In other words, the method may operate toperform parallel-beam scanning on the surface, where, depending on thecontrol algorithm used, the scanning may comprise raster scanning and/orvector scanning of the surface.

In a more detailed embodiment of the invention using reflective media,the system may include an energetic beam source, operable to emit anenergetic collimated beam, wherein the beam is operable to locally heatan illuminated region of the surface, and two optical devices, eachcomprising: a first reflective optical element, operable to rotatearound a first respective axis; a second reflective optical element,operable to rotate around a second respective axis, wherein the firstrespective axis and the second respective axis are parallel; and atleast one actuator coupled to the first and second reflective opticalelements, and operable to respectively rotate the first and secondreflective optical elements around the first and second respective axesin a coordinated manner such that the first and second reflectiveoptical elements are parallel, wherein the optical device is operable toperform a parallel displacement of the beam in a respective direction,and wherein the respective direction is orthogonal to the beam.

The two optical devices may comprises a first optical device and asecond optical device, where the first optical device may be operableto: receive the beam from the beam source; displace the beam in a firstdirection; and transmit the displaced beam to the second optical device.The second optical device may be operable to: receive the displaced beamfrom the first optical device; displace the beam in a second direction;and transmit the displaced beam to the surface, wherein the seconddirection is orthogonal to the first direction, and where the twooptical devices are operable to direct the beam to illuminate andlocally heat a sequence of specified regions of the surface to patternthe surface.

In another embodiment using a transmissive medium, the system mayinclude an energetic beam source, operable to emit an energeticcollimated beam, wherein the beam is operable to heat locally anilluminated region of the surface; and a parallel-beam scanner,comprising: a right prism comprising a refractive optical medium with anear face and a far face, wherein the optical medium has a specifiedindex of refraction, wherein the right prism is operable to: receive thebeam at the near face; transmit the beam to the far face; and emit thebeam from the far face, wherein the emitted beam is parallel to thereceived beam. The system may also include at least one actuator coupledto the right prism, and operable to rotate the right prism about aspecified axis to displace the beam in a specified direction, whereinthe direction, the beam, and the axis are mutually orthogonal, where theparallel-beam scanner is operable to direct the beam to illuminate andlocally heat a sequence of specified regions of the surface to patternthe surface.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention can be obtained when thefollowing detailed description of the preferred embodiment is consideredin conjunction with the following drawings, in which:

FIG. 1 illustrates a prior art system for scanning a surface,illustrating positional jitter or displacement jitter;

FIG. 2 illustrates parallel-beam scanning using a mirror pair, accordingto one embodiment;

FIGS. 3A and 3B illustrate embodiments of a system for scanning asurface using parallel-beam scanning in two dimensions via two mirrorpairs;

FIG. 4 illustrates parallel-beam scanning using a transmissive medium,specifically, a right prism, according to one embodiment;

FIG. 5 illustrates embodiments of a system for scanning a surface usingparallel-beam scanning in two dimensions via a right prism;

FIGS. 6A and 6B illustrate exemplary beam size manipulators usingreflective and refractive media, respectively;

FIG. 7A flowcharts one embodiment of a method for parallel-beam scanninga surface; and

FIG. 7B flowcharts a more detailed embodiment of a method forparallel-beam scanning a surface using reflective media.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and are herein described in detail. It should beunderstood, however, that the drawings and detailed description theretoare not intended to limit the invention to the particular formdisclosed, but on the contrary, the intention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the present invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Incorporation by Reference

The following references are hereby incorporated by reference in theirentirety as though fully and completely set forth herein:

U.S. Pat. No. 5,346,850, titled “Crystallization and doping of amorphoussilicon on low temperature plastic”, issued on Sep. 13, 1994;

U.S. Pat. No. 6,680,485, titled “Thin film transistors on plasticsubstrates”, issued on Jan. 20, 2004;

U.S. Pat. No. 6,509,217, titled “Inexpensive, reliable, planar RFID tagstructure and method for making same”, issued on Jan. 21, 2003;

U.S. Pat. No. 6,372,592, titled “Self-aligned MOSFET with electricallyactive mask”, issued on Apr. 16, 2002;

U.S. Pat. No. 5,885,904, titled “Method to incorporate, and a devicehaving, oxide enhancement dopants using gas immersion laser doping(GILD) for selectively growing an oxide layer”, issued on Mar. 23, 1999;

U.S. Pat. No. 5,840,589, titled “Method for Fabricating Monolithic andMonocrystalline All-Semiconductor Three-Dimensional IntegratedCurcuits,” issued on Nov. 24, 1998;

K. H. Weiner et al., “Low-Temperature Fabrication of P+-n Diodes with300-A Junction Depth,” IEEE Electron Device Lett. vol. 13, no. 7, pp.369-371 (July, 1992); and

P. G. Carey et al., “Fabrication of Submicrometer MOSFET's Using GasImmersion Laser Doping (GILD)”, IEEE Electron Device Letters, Vol.EDL-7, No. 7, July 1986.

Terms

The following is a glossary of terms used in the present application:

Memory Medium—Any of various types of memory devices or storage devices.The term “memory medium” is intended to include an installation medium,e.g., a CD-ROM, floppy disks 104, or tape device; a computer systemmemory or random access memory such as DRAM, DDR RAM, SRAM, EDO RAM,Rambus RAM, etc.; or a non-volatile memory such as a magnetic media,e.g., a hard drive, or optical storage. The memory medium may compriseother types of memory as well, or combinations thereof. In addition, thememory medium may be located in a first computer in which the programsare executed, or may be located in a second different computer whichconnects to the first computer over a network, such as the Internet. Inthe latter instance, the second computer may provide programinstructions to the first computer for execution. The term “memorymedium” may include two or more memory mediums which may reside indifferent locations, e.g., in different computers that are connectedover a network.

Carrier Medium—a memory medium as described above, as well as signalssuch as electrical, electromagnetic, or digital signals, conveyed via acommunication medium such as a bus, network and/or a wireless link.

Programmable Hardware Element—includes various types of programmablehardware, reconfigurable hardware, programmable logic, orfield-programmable devices (FPDs), such as one or more FPGAs (FieldProgrammable Gate Arrays), or one or more PLDs (Programmable LogicDevices), such as one or more Simple PLDs (SPLDs) or one or more ComplexPLDs (CPLDs), or other types of programmable hardware. A programmablehardware element may also be referred to as “reconfigurable logic”.

Program—the term “program” is intended to have the full breadth of itsordinary meaning. The term “program” includes 1) a software programwhich may be stored in a memory and is executable by a processor or 2) ahardware configuration program useable for configuring a programmablehardware element.

Software Program—the term “software program” is intended to have thefull breadth of its ordinary meaning, and includes any type of programinstructions, code, script and/or data, or combinations thereof, thatmay be stored in a memory medium and executed by a processor. Exemplarysoftware programs include programs written in text-based programminglanguages, such as C, C++, Pascal, Fortran, Cobol, Java, assemblylanguage, etc.; graphical programs (programs written in graphicalprogramming languages); assembly language programs; programs that havebeen compiled to machine language; scripts; and other types ofexecutable software. A software program may comprise two or moresoftware programs that interoperate in some manner.

Computer System—any of various types of computing or processing systems,including a personal computer system (PC), mainframe computer system,workstation, network appliance, Internet appliance, personal digitalassistant (PDA), television system, grid computing system, or otherdevice or combinations of devices. In general, the term “computersystem” can be broadly defined to encompass any device (or combinationof devices) having at least one processor that executes instructionsfrom a memory medium.

Galvanometer or Galvanometer Mirror—originally proposed and used by W.Thomson (Lord Kelvin), this is a type of actuator device in which atoroidal coil is situated between a pair of permanent magnet pole pieceswith its plane parallel to the magnetic field of the magnet. For a givencoil and magnet, the torque attempting to move the coil normal to thefixed field is proportional to the current through the coil. A mirror isaffixed to the coil. The mirror may be rotated, where the ultimaterotational range is 90 degrees. Kelvin's significant contribution wasshining a light on the mirror, which was then reflected to a scale.

Transmissive Medium—may be a lens or prism or other optical medium whichpasses, redirects, expands, or contracts a beam by transmission of thebeam through the medium.

Reflective Medium—any optical device which translates, expands orcontracts a beam by means of reflection, such as a mirror.

Parallel-Beam Scanning

It is the nature of a laser beam to exhibit a parallel character withextremely small divergence. In considering ways to perform scanning,this character may be used in a manner that delivers (sequentially)beams for each x-y position so that each is parallel to the optic axis,rather than divergent. The benefits of doing this are several. The arrayof beams may be fed into a beam shrinker, emerging as parallel beams ofsmall cross section and higher specific power, approximately by theratio of the area reduction. This control of power, or fluence, is asubstantial advantage. Another major advantage is thatshrinker-to-sample distance is rendered non-critical because the need tofocus an image on the sample is eliminated.

Raster Scanning with Parallel Beams

Using time-separated parallel beams of radiation for the pixel-by-pixeldelivery of a pattern to a surface brings the advantage that the“working space” between pattern generator and the patterned surface isnon-critical and can be large. This in turn is beneficial when, forexample, the surface to be patterned is in a confined space or a hostileenvironment (e.g. high-vacuum, toxic gas (such as arsine) or toxicsurface dopant (such as arsenic)). Eliminating in this manner the needfor lenses or focusing mirrors brings the further advantages that theseelements do not compete for space with other experimental necessitiesnear the surface, that the need for precise focusing is eliminated, andthat exotic or short-lived materials are not needed in, for exampleagain, lenses for short-wavelength radiation.

FIGS. 2-3B—Parallel-beam Scanning Using Reflective Media

FIGS. 2-3B illustrate parallel-beam scanning using reflective media,according to one embodiment. More specifically, FIG. 2 illustratesparallel-beam scanning in one dimension using reflective media, whileFIGS. 3A and 3B illustrate a scanning system comprising a parallel-beamscanner based on the principles of FIG. 2.

FIG. 2—Parallel-beam Scanning with Dual Mirrors

FIG. 2 illustrates a technique for parallel-beam scanning in onedimension using two parallel mirrors operated in a coordinated manner,according to one embodiment of the invention. As FIG. 2 shows, a beam101 may impinge on a first mirror 110A which is rotatable about an axis.The first mirror 110A may reflect the beam to a second mirror 110B, alsorotatable about an axis parallel to that of the first mirror. The secondmirror 110B may then reflect the beam to a desired target (not shown).

In this figure, solid lines denote the mirrors in their neutralpositions, which in some embodiments may be at 45 degrees with respectto the beam, and may correspond to beam incidence at the center of atarget, as well as the corresponding beam path. The dashed linesindicate the mirrors rotated from their neutral positions by 5 degrees,as well as the corresponding shifted beam path. Note that due to thewell-known principle that for a reflector the angle of incidence isequal to the angle of reflection, since the two mirrors are rotatedsynchronously and by the same amount, the resulting shifted beam (dashedline exiting second mirror) that exits the apparatus is always parallelto the original (neutral position) beam (solid line exiting secondmirror). Said another way, the fact that the two mirrors are rotated ina coordinated manner such that they remain mutually parallel results ina parallel displacement of a beam normal (orthogonal) to the axes ofrotation of the mirrors. Note that the displacement is also normal(orthogonal) to the beam itself. Note also, that the displaced beam isparallel to the original beam.

It should be noted that while the system shown in FIG. 2 operates todisplace a beam in only one direction, an additional pair of mirrors(with axes of rotation orthogonal to the axes of rotation of the firstset of mirrors) may be used to displace the beam in a second dimension.Thus, by deploying such coordinated mirror pairs in series,parallel-beam scanning over a plane (e.g., flat) surface may beperformed.

An exemplary embodiment of such a system is described below withreference to FIGS. 3A and 3B.

Note that the parallel shift or displacement of the beam increases asthe rotational angle increases, and decreases as the angle decreases.The useful range of angles should avoid the extremes, however, i.e.,near 0 degrees and near 90 degrees. Note also that as displacement isincreased by this method, mirror 110B must be increased in lateral sizeto ensure that it receives and reflects the beam from mirror 110A. Thevertical dimension of mirror 110B, however, need not be increased.Further, mirror 110A can me made quite small, because the source beamwill always be aimed at its center.

It should be further noted that for a given lateral dimension in mirror110B and increasing mirror separation, rotational range may have to berestricted so that the beam reflected from mirror 110A does not missmirror 110B. For any specific choice of some of these variables,allowable values and ranges for the remaining variable or variables maybe determined by employing a diagram like that of FIG. 2. No effort hasbeen made to show such details in FIG. 2 because its function is todisplay the principles of the invention.

FIGS. 3A and 3B—Exemplary Patterning System Using Reflective Media

FIGS. 3A and 3B are perspective diagrams illustrating an exemplarypatterning system utilizing reflective media, according to oneembodiment of the invention. As FIG. 3A shows, this embodiment includesa laser 100, a first pair of mirrors 112A and 112B, each operable torotate about a respective vertical axis 103, and a second pair ofmirrors 114A and 114B, each operable to rotate about a respectivehorizontal axis 105, as well as a target 108. Thus, this embodimentincludes two dual-mirror sets 112 and 114. As shown, beam 101 exits thelaser, impinges upon mirror 112A, is reflected to mirror 112B, then tomirror 114A, then to mirror 114B, which reflects the beam to target 108.The positioning of the mirror pairs determines the neutral lateraldisplacement (112A/112B) e.g. 1 centimeter, and the neutral verticaldisplacement (114A/114B), e.g. 1 centimeter. In preferred embodiments,the target may be placed such that the neutral position of the system(e.g., 45 degrees with respect to the incident beam direction)corresponds to beam incidence at the center of the target.

Note that FIG. 3A shows the first of the dual-mirror sets, specifically,mirrors 112A and 112B, in their neutral positions (e.g. at 45 degrees)indicated by solid lines, and with a coordinated deflection as well(e.g. at 5 degrees from neutral, or 50 degrees from the beam, asillustrated in FIG. 2), indicated by dashed lines. Mirrors 112A & 112Bthus serve to determine the lateral displacement, and mirrors 114A serveto determine the vertical displacement. From the second of the fourmirrors onward, i.e., mirror 112B, the resulting beam paths areparallel. That is, the lateral displacement of the beam just afterleaving the second mirror equals the displacement of the beam justbefore striking the target. The third and fourth mirrors (seconddual-mirror set 114) are in their neutral positions (e.g. 45 degrees).Note that an angular deflection by this mirror pair would causetranslation up or down of the target strike points from the neutralposition while maintaining the beam-parallelism conditions outlinedabove. The deflection of the beam is indicated by two beam paths thatdiverge at mirror 112A. The solid path indicates the beam path when allmirrors are in their neutral positions, while the dashed path indicatesthe resulting path when the first pair of mirrors are configured for alateral deflection, indicated by the dashed mirror positions in FIG. 3A.Note the parallel displacement of the beam shown and labeledaccordingly. This type of parallel shift, e.g., in each of twodimensions, may thus facilitate accurate scanning of a plane target.

Continuing the discussion of mirror size from the description of FIG. 2,it is noted that mirror 114A should preferably approximate the size andproportions of mirror 112B, but with the larger dimension in thedirection of the rotation axis this time. Finally, that larger dimensionshould be chosen for both dimensions of mirror 114B, since its coveragein a particular design, even when fully rotated, must cover the entiretarget field when mirror 114B is projected onto the target along anormal to the target plane.

Additionally, there may be other considerations. For example,near-grazing incidence should be avoided because it makes beamdisplacement too critically dependent on angle of rotation. Similarly,large separations between the mirror pairs is to be avoided since thiswould reduce the range of angles to be controlled, thus making preciseangular control critical. It should be noted that no effort has beenmade to show mirror size and shape details in FIG. 3A because itsfunction is to display the principles of the invention.

Thus, in one embodiment of the present invention, a highly collimatedbeam of radiation from a laser (including ultra-violet (UV) producinglasers such as Excimer lasers, UV lamps followed by a beam collimator,one or more laser diodes, etc.) may be used, although it should be notedthat other energetic beams and beam sources are also contemplated,including for example, lasers of various frequencies, etc. Reflectionfrom two pairs of coordinated moving dual mirrors preferably causes thebeam to sweep across the target “field.” ON-OFF control of the beam maybe used to determine which pixels (i.e., which regions of the target) inthe sweep are irradiated and which are not.

In some embodiments, the beam may be shut off while the mirrors assumepositions to start another sweep of the field from the original edge ofthe field, where the sweep may be vertically displaced from the first bythe width of the beam. Successive sweeps may be performed with furtherrespective vertical displacements, as is well known in the art of rasterscanning. When the full field has been scanned, the irradiated pixelscreate the desired two-dimensional pattern. Note that in variousembodiments, the On-Off control may be performed either by turning thelaser itself on and off, by using a shutter arrangement such as is donein ordinary optical cameras, or via any other means as desired.

While the above description is directed to a raster scan of the target,in other embodiments, vector scanning may be performed. In other words,rather than scanning a series of rows, e.g., from top to bottom, orcolumns e.g., from left to right, the system may operate to scan aspecified contour (curve) or series of contours, as is well-known.

Note that in some embodiments, the order of the mirrors pairs may beswitched such that the horizontal displacement is performed prior to thevertical shift. Thus, one or more pairs of coordinated mirrors may beused to implement a parallel-beam scanner for treating or patterning asurface.

It may be desirable to employ a beam size manipulator between the secondmirror pair and the target, for example, to reduce the beam size forpatterning a very small area, or to increase the fluence so as, forexample, to highly heat and/or melt the surface. Such a beam sizemanipulator may be located inside the chamber containing the target(e.g. controlled environment at a specified pressure such as a highvacuum and/or a particular set of environmental parameters such astemperature, humidity, gas content) used to process the target, whichmay be advantageous so as to reduce the fluence of the energetic beamthrough the window between the external environment and the controlledenvironment (e.g. vacuum) chamber.

FIG. 3B illustrates the system of FIG. 3A, but with the addition ofcontrollers 120 and actuators 113 and 115. As FIG. 3B shows, thecontroller or controllers may be coupled to and control the actuatorsand the beam source, e.g., laser 100. For example, the controller orcontrollers 120 may operate to turn the laser on and off as needed, andmay also move each mirror pair in a coordinated manner to achieve thedesired displacement of the beam (while maintaining the parallel natureof the beam as described above). In some embodiments, the controller orcontrollers may be implemented in any of a variety of ways, including,for example, using computers, embedded devices, and so forth.

As FIG. 3B shows, in this embodiment, actuators or actuator pairs 113and 115 are respectively coupled to each mirror pair to move the mirrorsin a coordinated manner per control signals provided by controller(s)120. In various embodiments, an actuator may be provided per mirror orper mirror pair. Note that any type of actuators may be used as desired,including for example, galvanometers, stepping motors, servos, andthermally or voltage controlled “shape memory” alloy-based devices,piezoelectric, and capacitive devices, among others.

It is noted that in preferred embodiments, the dual galvanometer mirrorsof the system have an edge dimension that is about 40% larger than thatof the target (heat-treated surface). This is because in the neutralposition, e.g. 45 degrees, sin(45 degrees)=0.7071; thus need 1/0.7071 orabout 1.414 (41.4% larger).

With respect to the application of a UV laser energy source forsemiconductor (e.g. silicon) surface heating, and the initial shaping ofthe laser beam before it strikes the dual mirrors of the presentinvention, mirror optics may be advantageous, especially in terms ofuseful life when used with UV, especially lower wavelength (higherenergy) UV. One may exploit design principles employed in reflectivetelescopes, as illustrated in FIGS. 2-3B. This has the advantage ofstraight-ahead optical path axis.

With this system, a pattern can be created which is energetic enough tomelt silicon with a laser of vastly less instantaneous power than ahigh-power excimer laser by raster or vector scanning with a beam ofsmall cross-section, taking advantage of the fact that scanning time ofa few seconds is eminently compatible with the patterning ofsemiconductor wafers (one application for this design). Commercialmirror systems to realize the dual mirrors are directly applicable inthis technique.

FIGS. 4-5—Parallel-beam Scanning Using Refractive Media

FIGS. 4 and 5 illustrate parallel-beam scanning using transmissive,i.e., refractive, media, according to one embodiment. More specifically,FIG. 4 illustrates parallel-beam scanning in one dimension usingtransmissive media, while FIG. 5 illustrates a scanning system with aparallel-beam scanner based on the principles of FIG. 4.

FIG. 4—Parallel-beam Scanning with Right Prism

FIG. 4 illustrates a technique for parallel-beam scanning in onedimension using a refractive transmissive medium, specifically, a rightprism of glass or other refractive optical medium. Note that as usedherein, the term “prism” refers to any solid of extrusion (constantcross-section) made of a transmissive medium, e.g., glass. In apreferred embodiment, the optical medium has a high index of refraction,as will be explained below. As is well known, a right prism comprises an“extruded” solid of constant cross-section with parallel end surfaces,referred to as near and far faces of the prism, normal to the long axisof the prism. Note that the prism may be of any cross-sectional shape(referred to as the prism shape) desired. For example, in oneembodiment, the prism may have a shape geometrically similar to thetarget shape, e.g., the prism may have a square cross-section if thetarget is a square silicon wafer. For purposes of illustration, acylindrical right prism is used in the embodiments described herein. Theends of the cylinder are plane, parallel, and polished.

Means are provided that permit the cylinder to rotate about orthogonal Xand Y axes that intersect mutually, meeting at the midpoint of thecylinder axis. Let the beam of radiation for the neutral position of thecylinder coincide with the cylinder axes. The point, then, at which thebeam strikes the entry face is fixed by simple geometry—the length ofthe cylinder and the angle of rotation. The path of the beam in theinterior of the cylinder is determined by an additional factor, theindex of refraction of the transmissive medium. The exit point of thebeam from the exit face is dependent on both factors, geometry andindex. Note that transmissive materials for UV radiation may pose aproblem, and one way to increase beam displacement, is to increasecylinder length

As FIG. 4 shows, beam 101 may impinge on a near face 212 of prism 210.Note that the prism is rotatable about an axis, where in this particularcase is normal to the plane of the figure. In this figure, solid linesdenote the prism in its neutral position, as well as the correspondingbeam path. As shown, the prism 210 in its neutral position results inthe beam 101 traveling straight through the center of the prism andexiting the far face 214 of the prism substantially unchanged. Thedashed lines indicate the prism rotated from its neutral position by 5degrees (not drawn to scale), as well as the corresponding shifted beampath. Note that due to the well-known principle embodied by Snell's Law:n ₁ sin θ₁ =n ₂ sin θ₂  (1)where n₁ is the refractive index of a first optical medium, n₂ is therefractive index of a second optical medium, θ₁ is the angle ofincidence (with respect to the surface normal) of light in the firstmedium impinging on a boundary with the second medium, and θ₂ is theangle of propagation (with respect to the surface normal) of thetransmitted beam in the second medium, the beam will exit the prismparallel to the beam direction at entry.

Thus, in the embodiment shown in FIG. 4, if we assume a refractive indexof the first medium (e.g., air) to be 1, and the refractive index of thesecond medium (e.g., glass) to be 1.5, the angle of propagation in theprism is approximately:θ₂=arcSin((n ₁ /n ₂)*sin θ₁)=arcSin(0.66667*sin(5°))=0.0582  (2)where the “equal” signs indicate approximate equality. Since the twofaces are rotated synchronously and by the same amount with respect tothe incident beam, the resulting shifted beam that exits the prism isalways parallel to the original (neutral position) beam. Note that theshift is always normal to the beam itself. Using standard trigonometricrelations, and letting R denote the length of the prism, thedisplacement d is:d=[R*Sin(θ₁−arcSin((n ₁ /n ₂)*sin θ₁)]/Cos(arcSin((n ₁ /n ₂)*sinθ₁))  (3)which, in the above case of a 5 degree rotation of the prism, andassuming the length of the prism R=1, is approximately 0.0291. Ofcourse, by increasing R and/or the index of refraction of the prism, theamount of displacement corresponding to a given prism rotation may beincreased.

It should be noted that while the system shown in FIG. 4 operates toshift a beam in only one direction, specifically, in the direction ofthe prism rotation, with a suitable actuator or actuators, the prism maybe rotated about an arbitrary axis, e.g., as a combination of an Xrotation and a Y rotation, thus facilitating parallel-beam shift ordisplacement in two dimensions. An exemplary embodiment of such a systemis described below with reference to FIG. 5. It should also be notedthat while the embodiments described with respect to FIG. 4 and FIG. 5rotate the prism about a pivot point located in the center of the nearface of the prism, in other embodiments, the pivot point may be locatedat the center of the prism, i.e., at the center of mass, i.e., themidpoint of the prism's primary axis, or elsewhere as desired. In otherwords, in various preferred embodiments, the axis or axes or rotationmay be located at any point along the centerline or primary axis of theprism.

FIG. 5—Exemplary Patterning System Using Refractive Media

FIG. 5 is a perspective diagram illustrating an exemplary patterningsystem utilizing refractive media, according to one embodiment of theinvention. As mentioned above, in preferred embodiments, means areprovided that permit the prism (e.g., the cylinder) to rotate about twomutually orthogonal axes that intersect each other and that alsointersect a “pivot point” on the prism's (e.g., the cylinder's) axis,for example, the midpoint, or, alternatively, the center of the nearface of the prism, although other pivot points are also contemplated. Alaser beam or other collimated beam of radiation is fed into one face ofthe cylinder and out the other. Rotational manipulation of the prism(e.g., cylinder) about the aforesaid axes causes deflection (withoutdivergence) of the beam in two dimensions, so that raster scanning(and/or vector scanning) on a target surface can be achieved.

As FIG. 5 shows, this embodiment includes a laser 100, a right prism210, operable to rotate about a vertical axis 103 and a horizontal axis105, and target 108. As shown, beam 101 exits the laser, impinges uponthe near face 212 of the prism, is refracted to the far face 214 of theprism, and exits the prism to target 108.

Note that FIG. 5 shows the prism 210 in its neutral position (solidlines) and with a deflection or rotation as well (dashed lines). Notethat upon exiting the prism the beam path is parallel to the incident oremitted beam. That is, the lateral displacement of the beam just afterleaving the far face of the prism equals the displacement of the beamjust before striking the target. The deflection of the beam is indicatedby two beam paths that diverge at the point of incidence on the nearface 212. The solid path indicates the beam path when the prism is inthe neutral position, while the dashed path indicates the resulting pathwhen the prism is rotated, indicated by the dashed prism position inFIG. 5. Note that in this exemplary embodiment, the prism has beenrotated about both X and Y axes (about a pivot point located at thecenter of the near face of the prism), where the corresponding theparallel shift of the beam is shown and labeled accordingly. This typeof parallel shift, e.g., in each of two dimensions, may thus facilitateaccurate plane scanning of a target. It should be noted that in someembodiments, rather than X and Y rotations used in combination, anactuator (or actuators) may operate in spherical coordinates, e.g., witha direction of rotation, and an angle of rotation, together specifyingthe rotation and corresponding two dimensional beam shift. Otherrotational representation and control schemes may be used as desired.

Similar to the reflective media based embodiment described above withreference to FIGS. 3A and 3B, in one embodiment of the presentinvention, a highly collimated beam of radiation from a laser (e.g., aUV-producing laser such as an Excimer laser) may be used, although itshould be noted that other energetic beams and beam sources are alsocontemplated, including for example, lasers of various frequencies, UVlamps with collimators, one or more laser diodes, etc. Appropriaterotation of the prism preferably causes the beam to sweep across thetarget “field.” ON-OFF control of the beam may be used to determinewhich pixels (i.e., which regions of the target) in the sweep areirradiated and which are not.

In some embodiments, the beam may be shut off while the prism assumes aposition to start another sweep of the field from the original edge ofthe field, where the sweep may be vertically displaced from the first bythe width of the beam. Successive sweeps may be performed with furtherrespective vertical displacements, as is well known in the art of rasterscanning. When the full field has been scanned, the irradiated pixelscreate the desired two-dimensional pattern. Note that in variousembodiments, the On-Off control may be performed either by turning thelaser itself on and off, by using a shutter arrangement such as is donein ordinary optical cameras, or via any other means as desired.

As also described above, while the above description is directed to araster scan of the target, in other embodiments, vector scanning may beperformed. In other words, rather than scanning a series of rows, e.g.,from top to bottom, or columns e.g., from left to right, the system mayoperate to scan a specified contour (curve) or series of contours, as iswell-known.

Although not shown, the system of FIG. 5 is assumed to include acontroller and one or more actuators to rotate the prism and/or regulatethe beam. Note that, as with the reflective system, any type ofactuators may be used as desired, including for example, galvanometers,stepping motors, servos, and thermally or voltage controlled “shapememory” alloy-based devices, among others.

Thus, a parallel-beam scanner according to the present invention may beimplemented using reflective or refractive optical media. It should benoted that in further embodiments, combinations of these two techniquesmay also be used as desired.

In a preferred embodiment, the system may comprise a scannedUV-laser-beam system for the patterned heat-treating of a surface, e.g.,a silicon surface, such as a monocrystalline silicon wafer. For example,the beam may scan the surface using the techniques described herein,heating (and possibly melting) successive spots or pixels to facilitaterapid and efficient absorption of dopants, e.g., from a gas, into thesurface in a specified pattern, as described above with respect to theGILD method of deposition. In some embodiments, the system and methodsdisclosed herein may be used in conjunction with, or as part of, asingle-pumpdown fabrication system, as disclosed in U.S. Pat. No.5,840,589, which was incorporated by reference above. Note that theepitaxial growth of semiconductor layers and specific dopant layers canbe done with any technique which accomplishes the desired epitaxialgrowth, such as sputter-epitaxy as described in U.S. Pat. No. 5,840,589or molecular beam epitaxy (MBE) as is known in the art. Similarly,material removal can be accomplished by techniques such as ion millingsuch as described in U.S. Pat. No. 5,840,589 or other known techniquessuch as reactive ion etch (RIE).

Some Variants of the System

As noted above, various different techniques, components, andconfigurations may be used in embodiments of the present invention. Forexample, in some embodiments, the beam may be reduced (decreasing thespot size and increasing the fluence of the beam) and/or expanded(increasing the spot size and decreasing the fluence of the beam) priorto target incidence. Devices for manipulating the beam size aregenerally referred to as beam expanders and beam shrinkers. Note thatthe beam may be reduced and/or expanded prior to or after (or both),passage through the parallel-beam scanner (see FIGS. 3A, 3B, and 5).

FIGS. 6A and 6B illustrate exemplary beam reduction systems that may beused in or with embodiments of the present invention. More specifically,FIG. 6A illustrates a beam reducer that uses lenses, and FIG. 6Billustrates a beam reducer that uses mirror.

As FIG. 6A shows, in this embodiment, a positive or convex (convergent)lens and a negative or concave (divergent) lens are place in series,where the two lenses are matched to negate or revere each other'soptical effects. A laser operates to provide a beam incident upon thepositive lens. As is well known in the art of optics, the positive lensoperates to converge or focus the beam, thereby reducing the beam width,while the negative lens operates to diverge or expand the beam. Thus,upon exit from the positive lens, the beam converges toward the focalpoint of the lens. However, before the focal point is reached, thenegative lens receives or intercepts the converging beam and halts thebeam convergence, converting the converging beam back to aparallel-beam, but with a smaller beam width (and thus greater fluence)than when originally emitted from the beam source, as FIG. 6A clearlyshows. Thus, the beam size manipulator of FIG. 6A functions as a beamshrinker.

FIG. 6A also indicates possible positions for the parallel-beam scannerdescribed above with reference to FIGS. 3A, 3B, and 5. As may be seen,the parallel-beam scanner assembly may be located prior to, or after,the beam shrinker. However, due to the degrading effects of high fluenceupon optical elements (mirrors or lenses), it may be preferable to placethe parallel-beam scanner prior to the beam shrinker, so that the beamincident upon the mirrors has not yet been reduced or intensified.

Thus, a mated pair of negative and positive lenses, shown in mirror formin FIG. 6A, may be employed for the purpose of changing the diameter ofa collimated parallel beam. For use in patterning semiconductor wafers,the choice of a mated pair is used to adjust the laser beam fluence,which is important to effect the heating for solid-phase diffusion, orheating to melting point for liquid-phase diffusion (e.g. as in GILD).

FIG. 6B illustrates one embodiment of a beam shrinker that is a mirroranalog to the lens-based system of FIG. 6A. As FIG. 6B shows, in thisembodiment, positive and negative mirrors corresponding respectively tothe positive and negative lenses of FIG. 6A are placed in the beam path.Note that in the case of mirrors, a positive mirror (with a positivefocal length) is actually concave, and is thus convergent, and anegative mirror (with a negative focal length) is convex, and is thusdivergent, as shown. Note also that the positive mirror has a hole

As indicated, the beam emitted from the laser impinges upon the positivemirror and is reflected as a converging beam to the negative mirror. Thenegative mirror reflects the converging beam, halting the convergence.The reflected (and reduced) beam, now parallel again, then passesthrough the hole in the positive mirror and continues toward the target.

As with the system of FIG. 6A, a parallel-beam scanner may be placedbefore or after the beam shrinker assembly as desired, as indicated bythe two dashed lines labeled accordingly.

Thus, beam shrinkers or expanders (or any other types of beammanipulator) may be used in conjunction with embodiments of theparallel-beam scanner described herein.

In further embodiments of the present invention, the parallel-beamscanner may be used in conjunction with any other diffusion schemes andtechniques as desired. For example, rather than Gas-Immersion LaserDoping (GILD), solid or liquid phase diffusion may be effected vialocalized heating and/or melting of the surface via embodiments of theparallel-beam scanner disclosed herein, thereby obviating thecomplexities of managing gasified dopants. Note that in preferredembodiments, the surface is a silicon surface, e.g., a monolithicsilicon crystal, although the techniques described herein are broadlyapplicable to the scanning of any other type of surface, as well.

Some Advantages of Embodiments of the Present System

One advantage of the present invention according to some embodiments isthat low-cost, compact, off-the-shelf components may be utilized thatcan operate inside a vacuum system. Alternatively, the laser andoptionally some of the optics may be outside of the vacuum system, andthe beam transmitted into the vacuum system through a UV-transmissiveand UV-tolerant window. This configuration may work particularly well iffinal beam sizing, e.g., reduction (which increases the beam intensity),occurs either just outside the window, or entirely within the vacuumsystem. Note that with this configuration, the optical power density perunit area, i.e., the fluence, at and through the window is much lessthan that needed to cause the solid-phase diffusion effect, or to meltthe surface of the substrate, or other thermal-related effects. In otherwords, the optical power is spread out over a larger area as it passesthrough the window, thus improving the effective life of the window.This is particularly facilitated by the scanning approach describedherein, as opposed to “whole chip” or “whole wafer” exposure techniques(e.g., using masks) typically used in surface patterning processes suchas chip manufacturing, since the total fluence needed is only that whichwill melt one spot-size or pixel of target surface. Moreover, leavingthe beam reduction step until inside the vacuum chamber further reducesthe degradation effects of high fluence on the window, as well asreducing the effect of small dust particles outside the vacuum—onlyinside the vacuum must the environment be clear of micron-sizedparticles; outside, prior to final beam reduction, elimination of larger(e.g. 10 micron particles) may be sufficient.

Another advantage of this approach over projecting a patterning image isthat the energy per unit time (i.e., power) required from the radiationsource is reduced substantially, e.g., by a factor equal to the numberof pixels in the image, as compared to a system in which a single sourcemust illuminate the entire field simultaneously. In many applications,this factor may be quite large, given that in the systems needed forLSI, VLSI and ULSI patterning, the number of pixels is at least onemillion. This reduction of necessary beam source power may allow low- tomid-powered beam sources to be used rather than the high-power sourcesgenerally required for patterning processes, and thus may besubstantially less expensive and safer to use. Moreover, any lenses (orwindows) that may be used in the system may remain usable longer due todecreased degradation normally caused by high fluence of the incidentradiation.

Thus, using coordinated paired mirrors may eliminate the above describedproblems related to displacement jitter and planar scanning, and mayprovide additional benefits as well. Some benefits of embodiments of thepresent system and method include, but are not limited to, thefollowing:

1. The system may treat an area measuring a fraction of a cm2 to a fewcm2;

2. The system may have a megapixel to gigapixel or greater resolution(i.e. capable of being used to sub-micron effective scanning spot size);

3. The beam may be of high intensity or fluence (sufficient to meltsilicon);

4. The process may be driven by a low-power to medium-power laser, e.g.,a milliwatt laser;

5. The system may use optics that:

-   -   a. may be lens-free, i.e., using reflective media (e.g.,        mirrors) only (see FIG. 3A);    -   b. may be mirror-free, i.e., using transmissive media only (see        FIG. 5);    -   c. have a wide working-distance range from optics to target,        e.g. from approximately one centimeter to one or more meters;        and    -   d. are “straight ahead” in the sense that beam direction is        essentially unidirectional. See for example, FIG. 3A, in which        the lateral beam segments can be small, e.g., centimeters or        less, compared to an overall beam length, e.g., a meter or more.        FIGS. 7A and 7B—Patterning a Surface

FIGS. 7A and 7B illustrate embodiments of a method for accomplishingreal-time patterning of a surface, using an optical arrangement thatobviates the least desirable features encountered in simple-galvanometerscanning. In principle embodiments of the present method are related tothe flying-spot electron-beam scanning used almost exclusively fordecades to create video images on the inner face of a CRT (televisiontube), in that a point of incidence on a target surface is moved overthe surface to energize (e.g., locally heat or melt) specified regionsor pixels on the surface (down to some specified depth).

FIG. 7A—High Level Flowchart of a Method for Patterning a Surface

FIG. 7A flowcharts a high level embodiment of the method. In variousembodiments, some of the steps shown may be performed concurrently, in adifferent order than shown, or may be omitted. Additional steps may alsobe performed as desired. As shown, this method may operate as follows.

First, in 702 a beam may be received from an energetic beam source,e.g., by an optical device, where the beam has an initial direction. Thebeam source may be any of various types of beam source, such as, forexample, a UV laser or other beam source, as described above. The beamis preferably a collimated radiation beam. In some preferredembodiments, a laser beam with a wavelength of approximately 193nanometers or 308 nanometers may be used. The beam is preferablyoperable to locally energize an illuminated region of a surface,referred to as a “pixel”, whose size is determined by the beam spotsize, i.e., the beam's cross-sectional area.

The optical device preferably includes one or more elements that arerotatable about one or more respective axes, and which may operate todisplace the beam in a direction orthogonal to the beam, where the beamdisplacement direction and magnitude correspond to the rotation(direction and magnitude). In preferred embodiments, the optical devicecomprises a parallel-beam scanner, various embodiments of which aredescribed above in detail.

In 704, one or more optical elements may be rotated about respectiveaxes to displace the beam in a specified direction orthogonal or normalto the beam, where the displaced beam is parallel to the received beam.

In 706, a respective region of the surface may be illuminated with thedisplaced beam, where the respective region corresponds to positions ofthe rotated one or more optical elements. For example, as describedabove in detail, the surface may comprise a silicon wafer, where theilluminated region may be heated and possibly melted to effect efficientdopant diffusion into the illuminated region. The dopant may be sourcedfrom the enclosing gas (as in GILD) or from a layer of dopant-containingmaterial, such as heavily doped silicon (e.g. with Boron or other P-typedopant, or Phorphorous or Arsenic or other N-type dopant) depositedusing sputter-epitaxy, or a spin-on dopant such as boron or arsenic.Note that as used herein, p-type and n-type semiconductor material maybe referred to respectively as type-1 and type-2 semiconductor material,or vice versa.

In 708, the method elements of 702-706 may be repeated to energize aspecified sequence of respective regions of the surface, therebypatterning the surface. In other words, the method may operate toperform parallel-beam scanning on the surface, where, depending on thecontrol algorithm used, the scanning may comprise raster scanning and/orvector scanning of the surface.

FIG. 7B—Detailed Flowchart of a Method for Patterning a Surface UsingReflective Optical Devices

FIG. 7B flowcharts a more detailed embodiment of the method of FIG. 7A,based on the parallel-beam scanner described above with respect to FIG.3A and FIG. 3B. More specifically, the method of FIG. 7B is performed bya system that includes a pair of optical devices, i.e., a first and asecond optical device, each operable to perform a parallel displacementof a beam in a respective (orthogonal) direction orthogonal to the beam,where the beam displacement direction and magnitude correspond to therotation (direction and magnitude). In preferred embodiments, the pairof optical devices (e.g., with corresponding actuator(s) and controlmeans) comprises a parallel-beam scanner, various embodiments of whichare described above in detail.

For purposes of explanation, assume three mutually orthogonal axes ordirections, X, Y, and Z, where Z is the axis or direction of thereceived beam. In this embodiment, the pair of optical devices (eachcomprising, for example, a coordinated pair of mirrors) correspondrespectively to displacements in the X and Y directions.

As noted above, in various embodiments, some of the steps shown may beperformed concurrently, in a different order than shown, or may beomitted. Additional steps may also be performed as desired. As shown,this method may operate as follows.

In 712, a first optical device may receive an energetic beam from anenergetic beam source, where the beam has an initial direction. As notedabove, the beam source may be any of various types of beam source, suchas, for example, a UV laser, UV lamp with collimator, one or more laserdiodes, or other beam source, preferably collimated. The first opticaldevice preferably includes a pair of reflective optical elements (e.g.,mirrors) that are synchronously rotatable about respective axes suchthat the reflective optical elements remain parallel to each other. Inother words, the respective axes of the reflective optical elements areparallel to each other, such that when each element is rotated by thesame angle, they remain mutually parallel. Note that since the firstoptical device is associated with (and is operable to effect)displacements in the X direction, the respective axes of rotation forthe reflective optical elements are actually aligned with the Y axis ordirection.

In 714, the reflective optical elements of the first optical device maybe rotated (e.g., about their respective (Y) axes, e.g., by one oractuators under the control of a controller) to displace the beam in aspecified direction orthogonal or normal to the beam, specifically, theX direction, where the displaced beam is parallel to the received beam.As noted above, the two reflective optical elements are rotated by thesame amount and stay parallel. As described above in detail withreference to FIG. 2, this allows the beam to be displaced in a directionorthogonal to the beam direction, while keeping the displaced beamparallel to the original beam, i.e., the received beam of 712. Thedisplaced beam exits the first optical element and is transmitted to thesecond optical element.

In 716, the second optical device may receive the beam (displaced in thefirst direction) from the first optical device. Similar to the firstoptical device, the second optical device preferably includes a pair ofreflective optical elements (e.g., mirrors) that are also synchronouslyrotatable about respective axes that are orthogonal to the respectiveaxes of the first optical device, such that the reflective opticalelements of the second optical device remain parallel to each other.Note that since the second optical device is associated with (and isoperable to effect) displacements in the Y direction, the respectiveaxes of rotation for the reflective optical elements are actuallyaligned with the X axis or direction.

In 718, the reflective optical elements of the second optical device maybe rotated (e.g., about their respective (X) axes, e.g., by one oractuators) to displace the beam in a specified direction orthogonal ornormal to the beam, specifically, the Y direction, where the displacedbeam is parallel to the received beam. As noted above, the tworeflective optical elements are rotated through the same angularsubtense and stay parallel, thus allowing the beam to be displaced in adirection orthogonal to the beam direction, while keeping the displacedbeam parallel to the original beam, i.e., the received beam of 716. Thedisplaced beam exits the second optical element and is transmitted tothe surface.

In 720, a respective region of the surface may be illuminated with thedisplaced beam, where the respective region corresponds to rotationalpositions of the first and second optical devices. For example, asdescribed above in detail, in a preferred embodiment, the surface maycomprise a silicon wafer, where the illuminated region may be heated andpossibly melted to effect efficient dopant diffusion into theilluminated region.

In 722, the method elements of 712-720 may be repeated to energize aspecified sequence of respective regions of the surface, therebypatterning the surface. In other words, the method may operate toperform parallel-beam scanning on the surface, where, depending on thecontrol algorithm used, the scanning may comprise raster scanning and/orvector scanning of the surface.

It should be noted that in various embodiments of the methods described,any of the techniques and devices disclosed herein may be used asdesired.

Although the embodiments above have been described in considerabledetail, numerous variations and modifications will become apparent tothose skilled in the art once the above disclosure is fully appreciated.It is intended that the following claims be interpreted to embrace allsuch variations and modifications.

1. A method for fabricating an integrated-circuit monolith that issubstantially monocrystalline and having parts that are substantiallylattice-matched, said monolith being three-dimensional in the sense thatit comprises two or more layers of circuitry, said method combining atleast the following technologies: a) sputter deposition or molecularbeam epitaxy (MBE) of a type-1 semiconductor material by using a type-1semiconductor target; b) sputter deposition or MBE of a small amount ofheavily doped type-2 semiconductor material by using a type-2semiconductor target; c) diffusion in selected areas of the type-2impurity by using an energetic beam source to emit an energeticcollimated beam operable to locally heat an illuminated region of asurface, and a parallel-beam scanner, wherein the parallel beam scannercomprises: two optical devices, each comprising: a first reflectiveoptical element, operable to rotate around a first respective axis; asecond reflective optical element, operable to rotate around a secondrespective axis, wherein the first respective axis and the secondrespective axis are parallel; and at least one actuator coupled to thefirst and second reflective optical elements, and operable torespectively rotate the first and second reflective optical elementsaround the first and second respective axes in a coordinated manner suchthat the first and second reflective optical elements are parallel,wherein the optical device is operable to perform a paralleldisplacement of the beam in a respective direction, and wherein therespective direction is orthogonal to the beam; wherein the two opticaldevices comprises a first optical device and a second optical device,wherein the first optical device is operable to: receive the beam fromthe beam source; displace the beam in a first direction; and transmitthe displaced beam to the second optical device; wherein the secondoptical device is operable to: receive the displaced beam from the firstoptical device; displace the beam in a second direction; and transmitthe displaced beam to the surface; wherein the second direction isorthogonal to the first direction; and wherein the two optical devicesare operable to direct the beam to illuminate and locally heat asequence of specified regions of the surface to pattern the surface,thereby performing said diffusion in the selected areas of the type-2impurity; d) removal of type-2 impurity from nonselected areas by ionmilling or reactive ion etching (RIE); and e) rapid annealing by usinggeneral (unpatterned) incident light.
 2. The method of claim 1, furthercomprising: repeating a)-e) one or more times to generate athree-dimensional doping pattern in the monocrystalline type-1semiconductor material.
 3. A method for fabricating anintegrated-circuit monolith that is substantially monocrystalline andhaving parts that are substantially lattice-matched, said monolith beingthree-dimensional in the sense that it comprises two or more layers ofcircuitry, said method combining at least the following technologies: a)sputter deposition or molecular beam epitaxy (MBE) of a type-1semiconductor material by using a type-1 semiconductor target; b)sputter deposition or MBE of a small amount of heavily doped type-2semiconductor material by using a type-2 semiconductor target; c)diffusion in selected areas of the type-2 impurity by using an energeticbeam source to emit an energetic collimated beam operable to locallyheat an illuminated region of a surface, and a parallel-beam scanner,wherein the parallel beam scanner comprises: a right prism comprising anoptical medium with a near face and a far face, wherein the opticalmedium has a specified index of refraction, wherein the right prism isoperable to: receive the beam at the near face; transmit the beam to thefar face; and emit the beam from the far face, wherein the emitted beamis parallel to the received beam; and at least one actuator coupled tothe right prism, and operable to rotate the right prism about aspecified axis to perform a parallel displacement of the beam in acorresponding direction, wherein the direction, the beam, and the axisare mutually orthogonal; wherein the parallel-beam scanner is operableto direct the beam to illuminate and locally heat a sequence ofspecified regions of the surface to pattern the surface, therebyperforming said diffusion in the selected areas of the type-2 impurity;d) removal of type-2 impurity from nonselected areas by ion milling orreactive ion etching (RIE); and e) rapid annealing by using general(unpatterned) incident light.
 4. The method of claim 3, furthercomprising: repeating a)-e) one or more times to generate athree-dimensional doping pattern in the monocrystalline type-1semiconductor material.
 5. A method for fabricating anintegrated-circuit monolith that is substantially monocrystalline andhaving parts that are substantially lattice-matched, said monolith beingthree-dimensional in the sense that it comprises two or more layers ofcircuitry, said method combining at least the following technologies: a)sputter deposition or molecular beam epitaxy (MBE) of a type-1semiconductor material by using a type-1 semiconductor target; b)sputter deposition or MBE of a small amount of heavily doped type-2semiconductor material by using a type-2 semiconductor target; c)diffusion in selected areas of the type-2 impurity by using an energeticbeam source to emit an energetic collimated beam operable to locallyheat an illuminated region of a surface, and a parallel-beam scanner,wherein the parallel beam scanner comprises: one or more optical media,operable to receive the emitted beam; and at least one actuator coupledto the one or more optical media, and operable to rotate at least one ofthe optical media around a respective specified axis to displace thebeam in a respective direction, wherein the respective direction, thebeam, and the respective specified axis are mutually orthogonal; whereinthe parallel-beam scanner is operable to direct the beam to illuminateand locally heat a sequence of specified regions of the surface topattern the surface, thereby performing said diffusion in the selectedareas of the type-2 impurity; d) removal of type-2 impurity fromnonselected areas by ion milling or reactive ion etching (RIE); and e)rapid annealing by using general (unpatterned) incident light.
 6. Themethod of claim 5, further comprising: repeating a)-e) one or more timesto generate a three-dimensional doping pattern in the monocrystallinetype-1 semiconductor material.
 7. A method for selectively scanning asurface, comprising: receiving a beam from an energetic beam source,wherein the beam is operable to locally energize an illuminated regionof the surface; rotating one or more optical elements about respectiveaxes to displace the beam in a specified direction orthogonal to thebeam, wherein the displaced beam is parallel to the received beam;illuminating a respective region of the surface with the displaced beam,wherein the respective region corresponds to positions of the rotatedone or more optical elements; and repeating said rotating and saidilluminating to energize a specified sequence of said respective regionsof the surface.
 8. A method for selectively scanning a surface,comprising: a first optical device: receiving a beam from a beam source;displacing the beam in a first direction, wherein the displaced beam isparallel to the received beam; and transmitting the displaced beam to asecond optical device; the second optical device: receiving thedisplaced beam from the first optical device; displacing the beam in asecond direction, wherein the displaced beam is parallel to the receivedbeam; and transmitting the displaced beam to the surface; wherein thesecond direction is orthogonal to the first direction; and the first andsecond optical devices respectively performing said receiving, saiddisplacing, and said transmitting to direct the beam to illuminate andlocally heat a sequence of specified regions of the surface to patternthe surface.